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Wegeners Theory: Continental Drift

His idea was that the Earth's continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other.

Evidence

the same types of fossilised animals and plants are found in South America and Africa

the shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle

matching rock formations and mountain chains are found in South America and Africa

Ideas Rejected Because

movement of continents not detectable, too big an idea from limited evidence, simpler explanations of the same evidence, Wegener an outsider to the community of geologists

Seafloor Spreading

In the centres of many oceans, there are mid-ocean ridges. At these places, thetectonic plates are moving apart. Molten material, known as magma from inside the Earth oozes out and solidifies. This movement of the mantle is referred to as convection due to heating by the core of the Earth. This process is called seafloor spreading. It results in seafloors spreading by a few centimetres each year.

earthquakes produce ...

a) P-waves (HT longitudinal waves) which travel through solids and liquids.

b) S-waves (HT transverse waves) which travel through solids but not liquids.